A set of rules for writing unit, integration, and component tests for a React project using Vitest and React Testing Library. TDD means writing tests before code, but these rules focus on testing user-visible behavior.

Use it when testing feature logic or user interfaces, including asynchronous interactions, accessible controls, and mocked API responses.

It guides developers toward tests that check real outcomes and important loading, empty, error, and success states instead of relying on fragile implementation details.

testing — Cursor rule by virastack

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add rules/virastack/ai/testing

Clone the repo

git clone --depth 1 https://github.com/virastack/ai

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.

When invoked 454 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00000	$0.00454
Opus 5	$0.00000	$0.00227
Sonnet 5	$0.00000	$0.00091
Haiku 4.5	$0.00000	$0.00045

Measured yesterday against content hash c8f758292527, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

testing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

templates/core/.cursor/rules/testing.mdc · 50 lines

What it actually says

Testing Guide (Pragmatic)

Principles

Value over Coverage: Focus on testing complex business logic in features/[feature]. Skip simple UI components unless critical.
Behavior Testing: Focus on user outcomes (Arrange-Act-Assert).
Accessible Queries: Prefer getByRole / findByRole (and label text) over test IDs so tests enforce keyboard-reachable UI.

Tech Stack

Vitest & React Testing Library.
Do not add Playwright/browser E2E unless the project already has it or the user explicitly asks.

Preferences (Not Hard Rules)

API: Use MSW for stable features; simple mocks are okay for rapid prototyping.
Location: Keep .test.ts next to implementation.
Snapshots: Use only for small, static data structures to prevent maintenance hell.
UI changes: For critical flows, cover loading / empty / error / success paths in RTL. Breakpoint and visual polish checks belong to the ui-components.mdc Delivery Checklist, not unit tests.

Mandatory Patterns

1. Async UI Testing (AAA Pattern)

ALWAYS use userEvent for interactions and findBy* for async assertions. Mock APIs via MSW.

// Act await userEvent.click(screen.getByRole('button', { name: /login/i }));

// Assert expect(await screen.findByText(/invalid credentials/i)).toBeInTheDocument(); });

Correct Implementation

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 50 lines · 0 tokens per session scan A c8f758292527

Subscribe to this mod's changes

testing is a cursor rule published in the GitHub repository virastack/ai (23 stars, last pushed 25d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 454 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Backend and APIs Frontend Testing agent-skills antigravity claude-code cursor skills virastack

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